Conventionally, research has been conducted related to optical elements which are equipped with a cell including two or more kinds of liquid that do not mix with each other (for example, an oil and a hydrophilic liquid), and which are operated (driven) by application of voltage. As such an optical element, for example, an optical shutter, a variable focal length lens, an image display device, and the like are known. In recent years, technology utilizing the electrowetting phenomenon has attracted particular attention.
As an example of the technology utilizing the electrowetting phenomenon, an electrowetting display (an electrowetting display device) has been disclosed that includes: a first substrate and a second substrate which are arranged so as to face each other; plural projections which define plural pixel units; an electrically non-conductive first fluid which is enclosed in a pixel unit between two adjacent projections; and a second fluid which is an electrically conductive or a polar liquid that is immiscible with the first fluid (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2009-86668).
Further, as an electrically conductive liquid for use in electrowetting display devices, an electrically conductive liquid is known that includes a specific polar solvent and a dye (a pigment, a dye, an oligomer dye, or a polymer dye) and has a total amount of monatomic ions of 500 ppm or less (see, for example, WO 2011/017446 and WO 2011/075720).
Further, it is known that impurities included in a dye for use in electrowetting display devices cause a back flow phenomenon at the time of image display and that, as the means to address this problem, a means of purifying the dye by silica gel column chromatography is effective (see, for example, J. Micromech. Microeng., 2009, vol. 19, page 65029).